I would say, no not essential, but helpful.
On an older tank I get away with a britta just fine. However, you do get more silicates, and may have a longer 'ugly' stage in the tank acclimatizing.
With RO water, you are adding less impurities, and with that feeding less things you don't want to bloom (like diatoms).
So yes it is possible, but it can be more work.
I'd say try it, and then for kicks you can get the RO water from one of those vending machines, and see if it makes your tank happier.